H 153 
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DEPARTMENT OF COMMERCE AND LABOR 
BUREAU OF FISHERIES 

GEORGE M. BOWERS, Commliatoiuf 



EFFECTS OF EXPLOSIVE SOUNDS, SUCH AS 

THOSE PRODUCED BY MOTOR BOATS 

AND GUNS, UPON FISHES 



Bureau of Fisheries Document No. 752 




WASHINGTON 

GOVERNMENT PRINTING OFFICE 

I9U 



DEPARTMENT OF COMMERCE AND LABOR 
BUREAU OF FISHERIES 



GEORGE M. BOWERS. Commissioner 



EFFECTS OF EXPLOSIVE SOUNDS, SUCH AS 

THOSE PRODUCED BY MOTOR BOATS 

AND GUNS, UPON FISHES 



't 

Bureau of Fisheries Document No. 752 




WASHINGTON 

GOVERNMENT PRINTING OFFICE 

I9U 



c^ 



3 



^ 



-b 



EFFECTS OF EXPLOSIVE SOUNDS, SUCH AS THOSE 

PRODUCED BY MOTOR BOATS AND GUNS, 

UPON FISHES 

y 

By G. H. Parker, S. D. 

Pro/eisor of /.oology, //amud I 'iiiiYrsity 



Bureau ot Fisheries Document No. 752 
9143° — 11 



EFFECTS OF EXPLOSIVE SOUNDS, SUCH AS THOSE PRODUCED BY 
MOTOR BOATS AND GUNS, UPON FISHES. 



By G. H. rARKKR, S. D.. 

Profcxxnr t)f Z'ltilor/ii. Iliirrtin} Vnirrrsily. 



SENSE OF HEARING IN FISHES. 

That sounds affect many fishes has hing heen recognized by fisher- 
men and naturalists. No less an authority than Izaak Walton de- 
clared that it shoidd be a rule \\\[\\ him to make as little noise as 
possible when he was fishing, lest he he heard and catcli no fish. 
Nevertheless it has been only within the last few years that the sense 
organs concerned with the reception of sound in fishes have been 
definitely identified. 

Using the term sound to include any vibrations of the water, from 
such slight movements as result from waves and currents to the 
vibrations that emanate from the impact of solid bodies under water 
or from the more violent discharge of explosives, it may be said that 
sounds affect fishes through three sets of sense organs — the skin, the 
lateral-line organs, and the ears. "Within recent years it has been 
demonstrated that a fish can feel sounds through its skin in much the 
same way that a human being can feel the vibrations of a musical 
instrument when his hand is in contac't with it. It has also been 
demcmstrated that certain fishes sense relatively low vibrations, such 
as trembling movements of the water, by means of the lateral-line 
organs. And furthermore, though this point has been disputed, it 
.seems clear to the writer through work carried out under the auspices 
of the Bureau of Fisheries that the internal ears of fishes arc not only 
organs for tlie adjustment of bodily motions and equilibrium, but 
also organs of hearing. 

THE QUESTION OF MOTOR-BOAT NOISES. 

If, then, fislies are sensitive tlirough so many channels to sounds, 
the question naturally ai-ises as to the eff'ect of the introduction oi 
motor boats and other sound-producing mcclianisms on the fislies of 

3 



4 EFFECTS OF EXPLOSIVE SOUNDS UPON FISHES. 

our shores. Are such devices favorable, inert, or prejudicial to our 
fi.sherios, and, if jirejudicial, in what ways can they be modified to 
make them least harmful? 

Motor boats driven by exploding gasoline are ecjuipped, as a rule, 
with an escape pipe which is situated close to the level of the water 
and through which the exploded gas is discharged in violent jets. 
This pipe is sometimes so arranged that its end may be dropped 
below the water level or kept in the air. 'Wlien the gas is delivered 
info flie air each discharge is usually accompanied by a familiar 
explosive noise of much penetration. "WHien the delivery is into the 
water the sound is greatly muffled and freed for the most part from 
its objectionable penetrating character. This method of reducing 
the noise is so easily applied that in certain communities efforts have 
been made to require all motor boats to be thus muffled, at least be- 
tween certain hours. The objection from the standpoint of the motor 
boats to this form of naiffling comes from the fact that when the 
es<;ape pipe is under water the ol)struction to the free outwaid pas- 
sage of the gases is so much increased that the efficiency of the 
motor is considerably reduced, and hence the running of the boat is 
unpaired. 

To the human ear under ordinary circumstances most motor boats 
either with or without mufflers are noisy appliances, generating 
soimds that are carried a long distance through the air. But in 
the water these sounds are very much less penetrating. To test 
this, a 7-horsepower motor boat with an exceptionally loud sound 
was run in ojoen water and an observer plunged under the surface 
as the boat passed. AAHien within 10 or 1'2 feet of the boat, whose 
escape pipe was in the air, the explosions of the gas could be faintly 
heard, though they were disagreeably loud to the observer when in 
the air. With the escape pipe under water and at the same distance 
as before the noise, of the explosions could scarcely be detected at 
all under water. Thus both methods of running the boat delivered 
into the water surprisingly little sound as compared with what 
escaped into the air, and of the two conditions the muffled boat 
yielded to the water much less sound than the unmuffled boat. 

In testing the effect of the motor-boat noises on fishes, a number 
of lands of fish known to be sensitive to sounds, sucli as killifish 
{Fvndxdus heteroclitiis) , young scup {Stenotomus chrysops), and 
young kingfish {.Venticirrhus saxatilis) were placed in a large 
wooden cage, 4 feet square by about 2 feet deep, whose walls were 
of strong netting. This cage was fastened in quiet water at the 
end of a float and a motor boat of 3| horsepower and with a pene- 
trating noise was started at a distance of some 400 feet from the 
cage and run at full speed past it. 



EFFECTS OF EXPL0SI\T; SOUNDS UPON FISHES. 5 

An observer was stationed on the float to note any response made 
by the fish. Tests were made with the escape pipe out of water 
and with it imder water, but in neither instance was there any ap- 
parent effect upon the fishes. Most of these fishes, and especially 
the killifish, go down into deeper water when only sliglitly dis- 
turbed, but in these trials they remained playing about on the sur- 
face of the water while the boat passed and were in no observable 
way disturbed until the swash from the boat struck the cage, where- 
upon they generally dove to the deeper part of the receptacle. 

Another test of a like kind was carried out on mackerel {Scomber 
scombnis). About 30 of these fish that had been for one or two days 
in a large pocket at the end of a pound net about a quarter of a mile 
from shore were gathered together by having the pocket pursed up 
into a space about 25 feet square and 10 feet deep. In this space they 
swam slowly about in a circle near the top of the water. 

When an observer stationed in a boat at the edge of the pocket rose 
in the boat the fish very usually went to the bottom of their inclosure, 
to return to the surface after the observer had taken his seat again. 
While the observer was sitting and watching the fi.sh a second per- 
son ran a motor boat over a circular course about half a mile in 
circumference, the course passing close to the pocket at one point. 
As the motor boat passed the pocket the fish were closely scrutinized 
by the observer. In no instance, either with the escape pipe of the 
motor boat above water or under water, did the mackerel sink into 
the deeper part of the pocket nor did they show in any other observ- 
able way that they were disturbed by the noise from the boat. Seven 
of them were then isolated in the cage previously mentioned and 
tested under close inspection by running the motor boat past the 
cage, but again the mackerel gave no evidence of being disturbed by 
the noise. 

Although these tests seem to be quite conclusive in showing that 
the faint noi.ses produced in the water by a motor boat have no 
marked effect on the ordinary activities of certain fishes, it is not 
impossible that the same noises may interfere with other activities 
of these fishes, such as feeding, pairing, egg laying, etc. The only 
tests in this direction that were carried out had to do with feeding. 
Plungry killifish, scup, and kingfish were placed in the cage pre- 
viously used and the cage was fastened to a float so that a motor 
boat could pass close to it. When the fish were feeding vigorously 
the motor boat was run bj' the cage several times, but in no case did 
the fish give up feeding in consequence of the noise. 

Another test was made with baited lines. Two baited fish lines 
were lowered from the edge of a wharf until the bait was about C> 
feet under water. In a short time the two baits were surrounded bv 



6 EFFECTS OF EXPLOSIVE SOUNDS UPON FISHES. 

dinners {Tautogolahrus adspet'siis), which began to nibble actively. 
A motor boat was now backed up under its own jaower from a dis- 
tance of about 50 feet till its stern was directly over the baited lines. 
During the approach of the motor boat the fishes continued to nibble, 
notwitlistaiiding the increasing noise, till the boat was within G feet 
of the lines, whereupon the fishes ceased nibbling. On running the 
motor boat away for a short distance, 6 to 8 feet, vigorous nibbling 
recommenced. It is difficult to say whether the cessation of nibbling, 
which regularly occurred when the stern of the boat was brought 
close to the lines, was due to the noise that reached the fishes or to 
the churning of the water in their neighborhood by the propeller of 
the boat. However this may be, it is certain that cunners can be 
driven from bait by a motoi- boat only when it is very close to them 
and that they are apparently uninfluenced by the same boat at a 
distance of 10 feet or so. 

If a cunner can be driven from bait by the disturbance from a 
motor boat close at hand, other fish may be affected in a like manner, 
and should these be more sensitive to noises than the cunners, it is 
possible that they may be influenced when boats are at greater dis- 
tances than C to 8 feet. There is, however, very little conclusive 
evidence on this point. In August, about the dock at Woods Hole, 
young bluefish (Pomatomus saJfatrix) are not uncommon. They are 
often angled for with rod and line and afford much sport for the 
local fishermen. They bite well, even with motor boats making 
much noise in the harbor and passing the dock at a distance of about 
a hundred feet. If, however, a motor boat comes close to the dock, 
they are almost certain to cease biting for a quarter of an hour or 
so. Observations of this kind are by no means conclusive, but 
they favor the opinion that some fishes are disturbed by the noises 
from motor boats, though these disturbances are always very tempo- 
rai'v and local. 

The noises pi'oduced by motor boats have only a slight and, local 
influence on fishes, not only because the noises that really get into 
the water are very faint, but probably because they reach the fish in 
the most favorable way for nonstimulation. Most persons who 
have experimented with the effects of sound on fishes have been struck 
with the fact that after a fish has responded once or twice to a given 
sound, it often ceases to respond to further stimulation for some 
considerable time, and in experiments of this kind it is usual to allow 
relatively long intervals of time to elapse between tests in order that 
the fishes may return to a receptive state. In the approach of a 
motor boat the sound that first reaches the fish must be far too faint 
to call forth any response, and this sound grows so gradually in 
intensity and with such rapid reiteration that the fish probably 
acquires the state of nonreaction to sound by the time the stimulus 



EPFECTS OF EXPLOSIVE SOUNDS UPON FISHES. 7 

has grown to such an intensity as would have been eftVetive liad a 
single shociv been delivered at once to the fish. The gradual ap- 
proach of the boat, then, does away with the element of contrast 
between silence and loud noise, and the result is just the reverse of 
that of summation, so often seen in the api^lication of minimal 
stimuli to sense organs; the fish fails to respond. 

RESPONSE TO THE SOUND OF GUNSHOTS. 

If this explanation of the general ineti'ectiveness of motor Ixiats 
in disturbing fishes is correct, then these animals ought to be re- 
sponsive at least to single, loud noises generated clo.se to the water. 
As long ago as 1782 Hunter demonstrated that fishes w^ere respon- 
sive to the discharge of a fowling piece. In his account of the in- 
ternal ears of fishes he states that — 

In the year 1762. when I was in Portugal. I ol)>iOi-vo(l in a nol)l('ninn's car- 
den near Lisbon a small fi-shpond. full of different kinds of flsli. Its liolioui 
was level with the ground and was made by forming a bank all nanul. Tlierc 
was a shrubbery close to it. Whilst I was lying on the l)ank, (jbserving the 
lish swim about. I desired a gentleman who was with mo to take a loaded 
gun and go behind the shrubs and tiro it. The reason for going behind the 
shrubs was that there might not be the lonst reflection of light. The instant 
the report was made the tish appeared to be all of one mind, for they vanished 
instantaneously into the mud at the l)ottoiii. raising as it were a cloud of mud. 
In .-ibout flvo miuutes after they began to appear, till the whole came forth 
again. 

It is, quite evident from this observation by Hunter that fishes 
can be disturbed by the discharge of a gini in the air, even when it 
is some distance from them. 

To test the efl'ect of single, loud noises on fishes several Fundulu^ 
were liberated in a cage, and after they had liecome quieted a fowl- 
ing piece was discharged a few feet fi'om them, but in such a posi- 
tion that they could not see it. At the report of the gun most of 
the fishes gave a single leap forward and to one side. This was 
several times repeated at considerable intervals and invariably with 
the same results. Bait was then thrown into the cage, and while 
the Fundulut! were busy tussling with this food (he gtni was again 
discharged. They immediately forsook the bait, but in half a miniile 
they had returned to it with full vigor. From these tests it is evi- 
dent that Fundtihis is easily disturbed by such a noise in the air as 
the discharge of a gun, but it is also evident that this disturbance 
is of a very temporary kind. 

To ascertain something of the strength of the sound stiunilus that 
caused the FundiduH to react an ob.server dove under tiie water, tind 
while he was there the gun was discharged in nnich the same rela- 
tion to him as it had Iteen to the fishes. Although the report of 
the gun in the air was almost ileafening, when it was heard under 



8 EFFECTS OF EXPLOSIVE SOUNDS UPON FISHES. 

a foot or so of water it resembled the pop of a soda-water bottle 
both ill quality and in intensity. This great reduction in intensity 
of the sound, as in the case of the motor-boat sounds, results from 
the reflection of most of the sound from the surface of the water, 
and hence its failure to enter the water. Yet the little that did enter 
the water sufficed to stimulate the fishes. 

Fu7idulufs is known to be quite sensitive to sound, but the fact 
that it lives under water renders it relatively inaccessible to sounds, 
since most sounds originate in the air. This explains why Fundulus 
and most other fishes fail to respond to the human voice. It is not 
that the human voice in itself is not strong enough to stimidate a 
fish, but rather that so little sound from it enters the water that 
stimulation is impossible. The .surface between water and air is for 
fishes an effective screen through which very little sound can pass. 

AVith the view of a.scertaining .something of the effectiveness of a 
gun report as a stimulus for Fundulus, trials were made by firing 
the gun at various distances from the cage of fish. Fundulus in- 
variably responded to the discharge of the gun at 100 feet from the 
cage; the_y usually responded at 200 feet; but they never responded 
at 500 feet. From these observations it is evident that the effect of 
the report of a gun is distinctly local and in this respect it re- 
sembles the motor-boat noises. 

It would be a matter of great interest to ascertain what influence 
the firing of hea\'_y guns has on fishes, but thus far no good oppor- 
tunity for prosecuting such investigations has been found. Through 
the courtesy of the commanding officer of the United States revenue 
cutter Greshani it was possible to study the effect of the explosion 
of a saluting charge of 2 jjounds of powder from a C-pound howitzer. 
In these tests a considerable number of Fundulus were retained in a 
cage and the tests made at varying distances from the gun. At 
2,000 feet no response was given to the report, and the same was 
true at 1,000 feet. Within 30 feet of the gun the conditions for 
accurate observation, because of the heavy detonation, were very 
unfavorable, but the response at this position was at most only 
momentary and certainly not more strilring than the reaction to the 
report from a fowling piece. 

From these observations it seems quite clear that single, loud 
noises generated in the air enter water to a small extent, but in 
sufficient volume to disturb momentarily fishes that are in the im- 
mediate vicinity. But even this limited disturbance does not seem 
to be produced by the ordinary motor boat which, partly because of 
the faintness of its sound under water and partly because of the 
grathial increase and decrease of the sound in intensity as the boat 
approaches and recedes, is relatively inert so far as many fish are 
concerned. 



EFFECTS OF EXPLOSIVE SOUNDS TPON FISHES. 9 

CERTAIN SOUNDS ATTRACTIVE TO FISHES. 

The j)i-oblein i>f the rehitiun of fishes to sounds is almost always 
taken up from the standpoint of negative reaction, in that it is as- 
sumed that noise drives fishes awav*. It must be remembered, how- 
ever, that there are fishes, like the drumfish and especially the 
squeteague, that produce noises which are without nuich douljt con- 
cerned with bringing the se.xes together in the breeding season and 
that these noises, therefore, are not repellent but serve to attract. 
Cases of this kind show that it is possible that even artilicial noises, 
if appi-opriate in character, might attract fishes, for sound, e\en 
when disagreeable to the human ear, is not of necessity always dis- 
turbing to fishes and might even serve as a lure. 

CONCLUSIONS. 

The sounds produced by motor boats are extremely faint under 
water and have little influence on the movements and feeiling of 
fishes. Such infiuence as they do have is temporary and very much 
restricted in local extent. 

Single explosive sounds, like the report of a gun, may startle fish 
and cause them to cease feeding, but these responses are also tem- 
porary and local. 

Although most sounds are repellent to fish, some may serve as 
lures to particular species. 

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